1. Field of the Invention
The present invention relates to marker lamps used on trucks or other automotive vehicles and particularly to marker lamps using light-emitting diodes as the light source.
2. Description of Prior Developments
It has recently been proposed to use light-emitting diodes as a light source in automotive vehicle marker lamps. Such diodes have the advantage of a relatively long service life, such that, in most cases, they will remain operable for the life of the vehicle on which they are installed. For example, U.S. Pat. No. 5,101,325 to Roney discloses a marker lamp employing light-emitting diodes as a light source.
The marker lamp shown in Roney has five light-emitting diodes arranged in a line or row with the endmost diodes being divergent and acutely angled to the plane of the lamp assembly in opposite directions, and with the centermost diode extending normal to the lamp assembly plane. The other two diodes diverge from each other to a slight extent so that the five diodes have a fan-shaped pattern, as shown in FIG. 1 of the patent drawings.
The fan-shaped array of five light-emitting diodes in Roney produces a multi beam output that is relatively wide in a plane taken along the row of diodes, and relatively narrow in the transverse plane. This is apparently designed to meet a U.S. Department of Transportation requirement for an output beam that has a horizontal divergence of at least 45.degree. in a horizontal plane and a vertical divergence of only 10.degree..
Prior to the present invention, it has been proposed to use rib-type prisms for spreading light beams produced by a single light source. U.S. Pat. No. 1,460,834 to Arbuckle shows an automotive headlight that includes a single light source in conjunction with a parabolic reflector 11 for directing parallel light rays against a flat lens having three sets of prism ribs at different points along the lens surface.
Another patent disclosing rib-type prisms for spreading light rays is U.S. Pat. No. 4,462,068 to Shadwick. In this case, the prisms are of incrementally varying angulations with the angulations of adjacent prism ribs differing by about 1.degree.. The lamp construction of the Shadwick patent is designed to produce a relatively even light pattern symmetrical around the lamp central axis.
U.S. Pat. No. 3,366,787 granted to Kelley shows a lamp construction wherein at least one lens wall of the lamp housing has different groups of prism ribs arranged to compensate for different angulations of the light rays impinging on different areas of the lens wall. By selecting different prism rib angulations at different areas of the lens wall, the patentee is able to achieve parallelism in the light rays emitting by the lens wall.
U.S. Pat. No. 4,733,335 to Serizawa discloses a vehicle lamp that includes an array of light-emitting diodes aligned with a lens system having a series of individual, semi-spherical condenser lens elements and diffusion lens elements arranged to evenly diffuse the individual light beams generated by the diodes. The aim of the lens system is to produce an essentially even light intensity across the exit face of the lens system.